Why calling Greenfield Lake green isn't all bad these days

Tuesday

May 10, 2011 at 4:24 PM

But officials cautioned to keep the recorded changes in perspective; the lake's water quality remains poor.

By Gareth McGrathGareth.McGrath@StarNewsOnline.com

Here's something you don't hear everyday; Greenfield Lake is getting healthier.Yes, that's right. The 90-acre Wilmington lake that drains nearly 2,500 acres and often lives up to its name with a green mat across its surface is, well, improving.But officials cautioned to keep the recorded changes in perspective; the lake's water quality remains poor.Still, considering what it was like not so long ago, the changes are noticeable and welcome."We're optimistic that it's going to get a little bit better each year," said researcher Mike Mallin, whose Aquatic Ecology Laboratory at the University of North Carolina Wilmington monitors the lake's water quality.Dave Mayes, head of the city's Stormwater Services, said the improvements haven't occurred overnight."We've been hard at it for a number of years, so it's nice to see that change," he said.Enhancing the lake's health didn't come easy, in large part because of Greenfield's presence smack in the middle of the Port City and its decades of slow deterioration.The lake's watershed has 36 percent impervious surface, meaning more than a third of the area is covered by roofs, driveways, streets and other solid materials that don't allow water to seep into the ground.The result is often massive sheets of water flowing into the six tributaries and other ditches that flow into Greenfield Lake, picking up all sorts of nasty pollutants from animal feces and fertilizers to motor oil and random trash along the way.Not so long ago, the flow of nutrients into the old mill pond led to huge mats of algae and vegetation blooms choking the waterway.During some especially severe outbreaks in 2003 and 2004, an estimated 95 percent of the lake's surface was covered by aquatic vegetation, according to UNCW researchers.While an eyesore, the green mats weren't just an aesthetic problem – although the lake is a centerpiece of the annual Azalea Festival.Fish and other organisms need dissolved oxygen to survive. But algal blooms are a telltale sign of insufficient oxygen."If you don't have good oxygen levels in the water, the fish can't breathe, other critters can't breathe, and you end up with fish kills," Mayes said.So in 2005, with public frustration running high, the city decided to take get aggressive.Moves over the years since have included releasing hundreds of sterile grass carp into the lake to munch on the floating vegetation, adding water-circulation systems to force dissolved oxygen to the surface, and periodically spraying aquatic herbicides.Comparing pre-2005 water quality data to more recent data, Mallin said the restoration efforts have showed steady improvements on most fronts.Sure, the droughts of recent years probably helped reduce the nutrients getting washed into the lake.But Mallin said the city's efforts have helped knock back some of the more severe problems afflicting the lake."I think it's helped a lot, put it that way," he said.But the lake isn't totally out of the proverbial woods yet.Fecal coliform levels remain stubbornly high, although levels in 2010 were the lowest in several years.Mallin said dog waste, and to some degree feces from waterfowl, are the culprits.Mayes said getting people to do the right thing – in this case pick up after their pets – is a work in progress."Education remains our primary tool," he said, although he added the city does have an ordinance mandating pet owners carry a doggie bag when out with Fido.Work on stopping contaminants washing into the lake's feeder creeks remains, well, a work in progress.And tight budgets could potentially reduce or stop the roughly $25,000 a year, not including some capital costs, the city spends on maintaining the centerpiece of its largest park.But Mayes said the long-term goal of getting Greenfield Lake off the state's list of impaired waters is no longer just a pipe dream."We're not there yet," he said, noting that algal blooms in the spring and early summer are still semi-common occurrences. "But we're headed in the right direction."